The present disclosure relates generally to systems and methods to improve the print quality of scan printing by reducing banding artefacts of an image on a substrate.
An ink jet printer generally includes a mechanism for moving print media along a media path. In scan printing, the printhead carriage typically moves laterally with respect to the print media, making several passes to complete an image printing process. During a scan printing operation, media is moved along the media movement path into a printing position, stopped and then the printhead carriage is moved perpendicular to the media movement path to eject ink droplets onto the media surface to create a band of ink dots, subsequently repositioning the printhead or the media by a defined distance, and then depositing another band of dots. If an error occurs in the media movement, for example as often is the case when printing on fabric, the resulting position of ink droplets on the media will be offset from the intended position, which results in undesired banding artefacts in the printed image. Because the banding artefacts tend to be repeated and parallel, these banding artefacts tend to be visible, reducing the overall quality of the image. For example, where the ink droplets were offset from the intended position, errors may show up as lines, bands, or gaps in the resulting image.
Several solutions have been developed to address the problem of banding artefacts such as move the printhead precisely or, more commonly, the media between scans. For example, some high-quality and finely-tuned machinery may reproducibly move a substrate over a precise distance and avoid banding problem, but the high cost and maintenance demands of such a system are problematic. Some solutions involve the use of a movement-tracking encoder. In those setups, either a radial or linear encoder supplies the system with information about how much a component of the system which is in contact with the media actually moves, the feedback from which allows for more precise movement. This approach is problematic in that it is typically some reporter device, such as a sensor along a refractive strip or spinning disc, that is observed moving rather than the media itself. As such, supplying different media with different stretch properties or thicknesses may result in an error in the media movement. Additionally, such systems need to be re-calibrated for each new type of media used.
Another approach to reduce the printed banding problem is to attach an encoder to the media itself. This is frequently implemented as holes punched into the sides of media at regular intervals, such as some styles of printer paper. The media may be moved directly by interacting gears with the holes, or the media may be moved by some other means and motion monitored by sensors, such as light emitters on one side of the column of holes and a photo-sensor on the other side. A notable cost of this method is that media must be modified prior to printing, which in turn raises media prices and reduces the choice of compatible media to the consumer.
The technique of multiple printing passes during which image ink droplets are overlapped has been used to reduce the appearance of media feed error. However, this technique increases printing time for a given image because of the number of printing scans required. Another method of introducing a random minute vibration between the printhead and the media during a printing pass has been used to reduce the banding artefacts. However, these approaches tend to decrease the overall resolution quality of the printed image.
Thus, there clearly exists a need to improve the image quality of images printed by scan printing.